1. FIELD OF THE INVENTION
This invention relates generally to inventory systems, and more specifically to a method for locating and retrieving a randomly placed object.
2. DESCRIPTION OF THE PRIOR ART
The use of automated inventory and retrieval systems has become a necessity for many large-volume processes in which a large number of items must be stored for a period of time. Such processes include assembly line operations wherein a large number of identical items are temporarily stored prior to subsequent non-identical processing as well as retrieval systems where a large number of unique items must be stored in a manner such that quick retrieval is allowed.
In the prior art, an apparatus and method for positioning a vehicle at a storage bin in an automated storage and retrieval system is disclosed in U.S. Pat. No. 4,415,975, Burt. A retrieval vehicle is positioned at a storage bin in a three-dimensional rack structure containing objects in discrete storage bins of the rack structure. The method described by Burt allows precise positioning of the retrieval vehicle given an already known location of the stored object. This known method, however, requires a rigid rack structure, and presupposes that the location of the stored object in the rack structure is already known. Frequently, however, storage areas do not contain rack structures nor are the storage locations of the objects already known so as to allow positioning of a retrieval vehicle. For example, in steel finishing facilities, steel coils are temporarily stored in a random manner in production or storage bays in any available space.
In the manufacture of various alloy products, such as stainless steel sheets or silicon steel sheets, the product at several intermediate stages of production and the final product is in the form of a coil. These coils are placed in holding areas next to the production units and/or, when space permits in-storage bays prior to further processing or, after processing is completed, prior to shipment to a customer. To move the coils, use is often made of an overhead crane. The overhead crane embodies a crane bridge that moves through the bay warehouse along parallel tracks thereby providing movement back and forth in one direction. The crane further embodies a crane trolley that moves horizontally along the crane bridge in a direction of travel perpendicular to that of the crane bridge, thereby providing movement back and forth in a second direction. The crane bridge and trolley allow the overhead crane to be positioned above any area in which coils can be placed. The trolley has a reel that allows raising and lowering of an object fastener such as a hook or a magnet, for example. The object fastener is connected to the trolley by a cable and the object fastener is raised and lowered by winding and unwinding hhe cable connected to the reel of the trolley.
In conventional practice, coils are placed in rows, and, in some storage areas, a second and even third layer of coils are stacked vertically. Each coil is identified by a tag affixed thereto, or by markings directly on the coil. Unfinished coils may be selected for further processing in a specific order on the basis of the requirements of the next process. For example, different coils may be selected so that the width of strip in a rolling mill progressively decreases between successive coils, or to allow progressive increase of the acidity of a liquid in tubs of a pickling line.
In conventional practice, a particular coil is located by a person, called a stocker, who moves on foot through the storage area and manually locates each of the required coils. When the coil has been located in this manner, the person then signals a crane operator to position the crane above the coil. If the crane is not available to pick up the coil, the coil is marked on the top thereof for identification and later retrieval by the crane operator. This is a cumbersome, unsafe, and time-consuming operation. Consequently, the production schedule for further processing of coils frequently cannot be maintained because the coils cannot be located and retrieved in an expeditious manner.
It is accordingly a primary object of the present invention to provide a method for locating and retrieving randomly placed objects without requiring manual discovery of their location.
A further, more specific object of the invention is to provide a method for locating coils so that a coil can be picked up by an overhead crane wherein the crane bridge, trolley, and object fastener may be moved to the proper position for pickup of the desired coil without manually locating the coil and subsequent signalling to the crane operator with respect to the location of the coil.